Two-stage fluid-suspension roasting of iron sulfide ore



March 12, 1957 J. w. swAlNE ErAL 2,785,050

TWO-STAGE FLUID-SUSPENSION ROASTING OF IRON SULFIDE ORE Filed Aug. 21,1952 mv Tv mdfxm.: dmImDdu NN mw QN m mm w m4 mx dOFQuJJOU umn-2 0 R SEJRN q Y OIN E TAA N NWO R ESL O WNS a@ n .ISC A WN H Y @E vw vTwo-STAGEFLUID-SUSPENSION RoAsTIN'G oF' i IRoN sULFmE oRE ApplicationiAugust 21,1952, Serial No. 305,643

Claims. (Cl. 2.3-177)` This invention relates to the treatment of'sulfide ore and more particularly, refers to a new and improved processfor converting metal sulfides into SO2 gas and metal oxides.

Frasch sulfur is probably the cheapest source of raw material forconversion into SO2, S03 and H2804. Unfortunately, this raw material isin short supply. Consequently industry has intensified its efforts toprovide other means to meet the demand for sulfur oxides and sulfuricacid and to improve known methods of producing sulfur dioxide andsulfuric acid. There are available vast deposits of naturally occurringsulfur ores, particularly iron pyrites and pyrrhotite, the formerconsidered to have the empirical formula FeSz and the latter, FeS, FeiSsor FeioSn, dependent on the mine from' which it was derived. Sulfur andsulfur dioxide have been, and are to some ex'- tent, commerciallyproduced from iron pyrites and pyrrhotite, usually when Frasch sulfurwas not available at an economical price, as for example when freightbecomes a large item of cost due to the necessity of shipping the sulfura far distance to the site ofthe sulfuric acid plant.

Two methods are commonly employed in industry for roasting metallicsulfide ores; the so-called bed and suspension roasting operations. Thebed process has the drawbacks of requiring the use of mechanicallyoperated hearths of complicated construction and operation involvingconsiderable initial and maintenance expense. Also, the cinder productresulting from bed roasting frequently is incompletely oxidized andcontains an amount of sulfur making the cinder unsuitable for reductionto iron. Cinder having a high sulfur content,'roughly in excess of 1%sulfur, has negligible sales value and for all practical purposes is aWaste product and a nuisance. Thus, to make ore roasting commerciallymore attractive, it is desirable to produce a low sulfur cinder whichcan be disposed of readily at a value to compensate, `at least in part,for the cost of conducting the roasting operation.

Suspension roasting involves roasting ore -in vnely 'divided state whilein gaseous suspension vin an oxidizing gas such as air.Suspension'roasting 'is' advantageous over bed roasting in that lesscomplicated apparatus and operation are required and, of greatimportance, more complete oxidation of the ore can be attained toproduce a cinder suiiciently low in sulfur content to adapt it forreduction to metallic iron. However, in order to successfully roast orein a suspension burner, it is necessary to reduce the ore to finelydivided particles of the size' of about 40-60 mesh orsmalle'r. As'recognized in' the 4"afrt, grinding of ore to such a fine state is avery costly roperation and, consequently, suspension roasting haslimited application. Generally, suspension roasting has been foundeconomical only when there is available a supply of ilotationconcentrate which is a by-product from the milling in a mining operationand consists of pyrites orpyrrhotite' of 40mesh down to300 mesh orlower. I

' One object of the 'present invention is tolprovideman efiicient,economical, continuous" process for converting United. ,Parent 2metallic sulfide ores into sulfur dioxide and cinderlo in sulfurcontent.

Another object of this invention is to provide animproved method ofcomminuting, elutriating and drying sulfide ore. t A further object ofthis invention is to provide improved means and method in a unitarysystem of converting ore of large .particle size to a finely dividedstate and concomitantly roasting the ore to produce sulfur dioxide andcinderv adapted for use in reduction to metallic iron.

Further objects and advantages will be apparentfrom the followingdescription and accompanying drawing.vv

In accordance with the present invention, elutriation, drying,preheating, partial oxidation and comminuting o f' ore may besimultaneously accomplished by continuously introducingore into anenlarged vertical zone at a rate sucient to maintain a bed of solidstherein, continuouslyA passing a stream of air upwardly through the bedof solidsV at a velocity suiciently high to maintain substantially allrof thesolids in the bed in a iiuid state, and to suspend in the streamof air, solids of particle size not greater than 40 mesh, continuouslydischarging from the enlarged zone the stream of gas containingsuspended therein the finely divided particles of ore, withdrawing aportion of the large size particles-'ot ore from the bed in the enlargedzone,

crushing said large sizetparticles, returning said crushed ore to theenlargedzone for further contact with the upwardly rising stream of airtherein, and regulating the rate of introduction of ore and air into theenlarged zone soas to maintain therein a temperature in excess of about800"Y F. and below about l800 F., preferably between 1300 F. and 1500F., thereby effecting elutriation, drying and partial roasting of theore.

A specific embodiment of the invention comprises introducing ore into anenlarged vertical zone in an amount sufficient to maintain a bed ofsolids therein, maintaining the bed of solids in a duid condition bypassing a stream of gas upwardly through the bed of solids at a velocitysuiciently high to carry in suspension substantially only particles ofore of a size not in excessv of 40 mesh, removing a portion of the bedof solids containing large particles of ore, crushing said largeparticlesl of ore and recycling said crushed ore to the enlarged zonefor further contact with the stream of oxidizing 'ga-s, regulating therate of introduction of ore and. oxidizing gas into the enlarged zone tomaintain therein a temperature between about l300 F. and 1500" F.,thereby effecting drying and partial roasting of the ore, discharg-l inghot gases containing suspended finely divided par-V ticles of oresubstantially not in excess of 40 mesh size. from the space above thefluid bed of solids in theenlarged zone, passing the hot gasescontaining suspended particles of ore together with additional airupwardly through a second enlarged zone, regulating the introduce tionofk additional air into the second enlarged zone to maintain atemperature of about 1800 F. therein andi to effect substantiallycomplete oxidation of the Vsus-I pended particles of ore, dischargingthe SO2 containing; gasesk and roasted ore from the enlarged zone,separat-.l ing the cinder from the gases, cooling the SO2 containing;

gases, recycling a portion of the cooled SO2` containing'l gases tothesecond enlarged zone to aidin maintainiiigfA theI temperature therein,/and introducing another por-` tion of the cooled SO2 containing gasesinto the bottoni; ofthe first enlarged zone to provide a suicientlyhigh@ velocity to maintain the bed of solids in a fluid condition and toelutriate therefrom finely divided particles` of ore.

The accompanying drawing is a diagrammatic .fiw; sheet illustrating onemethod of. practicing thevprese'n't; inventionf Y, j. Referring to thedrawing, raw, untreated ore consist'-L v Y ing Yof iron pyritesorpyrrhotite or a mixture of both,

crushed to a size desirably not exceeding 1/2 in diamctcr, istransferred by conveyer 1 into feed hopper 2. Ordinarily, the raw,untreated ore from the mine is crushed to a particle size not exceedingabout 1/2" diameter, a relatively inexpensive operation,and the crushedore loaded in open freight cars and then shipped to the refinery forroasting. Such ore contains appreciable amounts of moisture, naturallyoccurring or resulting from exposure to weather conditions in transit.From past experience, it has been found that ore containing moisture inexcess of about 0.3-0.5% by weight of the ore causes agglomeration ofthe particles of ore which when subjected to roasting do not remain insuspension and are incompletely roasted resulting in high-sulfur cindernot satisfactory for reduction to iron. Thus, ore, to be successfullyroasted in a suspension burner, must be preliminarily treated to reduceit to a fine particle size and also dried to a low moisture content.

"`The raw ore, equal in amount to the desired feed rate in a suspensionburner, is charged into the system through aV pressure seal-type screw 3down through conduits 4 and 5 into uidized-elutriation and dryingchamber 6.

. A chamber 6 of about 4-10 feet in diameter will be satisfactory formost commercial operations. The raw ore is immediately mixed into thebed of solids 7 contained in chamber 6 by the violent turbulent actionof the bed. A portion of the oxidizable content of the ore reacts withoxygen contained in the uidizing gas passing upwardly through the bedand sufficient heat is generated to raise the bulk temperature of theore particles and gas leavingv they top of chamber 7 through conduit 8to a temperature in excess of 1300 F.

Fluidizing and oxidizing gas, preferably air, enters from the atmospherethrough line 9L and is forced by blower 11 through line 12 into thebottom of chamber 6, ,through screen support 13, and upwardly throughthe f l afsaozsov p y j 4 materially eifect iluidization, are density,shape, surface roughness, diameter, and size distribution grading.Merely by way of illustration, a linear gas velocity of 7-9 .feet persecond will elutrate and maintain in lluid condition a bed of ore solidshaving the following composition: f

Meshpsize: y

+4 e 2.7 -4-1-8 28.0 -8+l4 ...1 -..7.a 13.9

The amount of air, or more accurately, the amount of oxygen, should besuflicient to maintain the bulk tempcrature of the bedv 7 above theauto-ignition point of the ore, about 800 F., and below the sinteringtemperature, about 1800 F., in order to attain rapid drying bed ofsolids 7. The gas passing upwardly in chamber 6 through bed 7 should beat a suticiently high velocity to maintain the bed in a uid state andsimultaneously elutriate from the bed particles of ore not exceeding 40mesh size. This velocity will vary depending on the characteristics ofthe solids used, as will be now explained. Atlow gas velocities, the bedof solids remains fixed and the individual particles do not move. As thegas velocity is increased, a point is reached at which the bed becomesexpanded and is at the absolute minimum bulk density possible, about55-70% of original bulk density, without movement of the individualparticles relative to each other. This condition may be referred to asVthe state of incipient uidization. A slight increase in gas velocitywill then cause the bed to become fluidized with only insignificantcarry-over of the ner particles. As the velocity is further increased,action of the bed becomes more and more violent with the formation oftwo distinct phases: (a) a dense phase at the base of the vesselcontaining most of the solids, and (b) a dilute phase containing only arelatively small proportion of solids. Further increase in velocity willcause the densities of the dense phase and dilute phase to become equal,forming a single dispersed suspension similar to the nature of apneumatic conveying system. In the present invention, the velocitythrough the bed of solids 7 should be sutliciently high to maintain atleast two distinct phases, namely a lower dense phase and an upperdilute phase, and to carry over in suspension in the gas, particles ofore smaller than 40 mesh size. The formation of a dense phase and adilute phase in chamber 6 may be visually observed by means of sightglasses or by means of pressure differentials not shown in the drawing.Theproper The effect of characteristics of the solidsis and reactionrate, reduce explosion hazards and provide highly preheated feed to thesuspension burner, Preferred temperature range is between 1300 F. andl500 F. The system should preferably be operated under -superatmosphericpressureV because of simpliiied` gas handling requirements-a pressureVof approximately l to 2 p. s. i. g. will be found adequate. Excessivehigh pressures are unnecessary and add to the investment cost. Theamount of air required will be dependent in part upon the moisture`content of the ore, the quantity.V

As is ap- Y r the air intake of line 9 by means of valve 14 and blower V11. It it is` found that the amount of air introduced into chamber 7 isadequate to maintain the bed of solids 7 atV the desired temperature andto properly dry the ore therein, but insuflicient to elutriate the bedof solids 7, then a non-.oxidizing gas, as for example, recycle gas,which is primarily a mixture of nitrogen and SO2, is added throughconduit 15 to the stream of air entering through line 9 in an amountsuliicient to maintain the bed of solids 7 in a uid state'and toelutriate tine particles therefrom. Complete oxidation of the ore inchamber 6 is not accomplished or desiredonly partial oxidation of theore is effected in chamber 6 and completion of oxidation occurs in thesuspension burner. Ordinarily, it will be found that -.40% of the totalair required for complete oxidation of the ore will be introduced intouidized chamber. 7 and 80-60% of the total air will be introduced intothe suspension burner. recycle gas up to entering through line 15, basedon the amount of air entering through line 9, will generally be foundsufficient to impart the required velocity of the gas stream moving Vupthrough the bed of solids 7 in chamber 6. As is conventional, samples ofthe stream passing through line 8 may be periodically withdrawn andanalyzed to make certain that the ore particles suspended in the gasstream are of sufficient fineness.

Attrition of the bed of solids 7 may be promoted by the addition of aninert grinding medium to the bed of solids. This material can consist ofsilica, alumina, silica carbide or other inert compounds in the form 'ofeither natural or manufactured shapes, which are substantially inert totemperature, corrosion and abrasion. Sizes of this mediurn are to begraduated within the limits of the largest particles which can beproperly agitated with the uidizng gas to the smallest particle whichwill not be carried out'ot the system by the exit gas, or stated anotherWay, the inert grinding material should be of a graduated Size to be ina uid state, but not elutriated from the bed of solids. Desirably, theinert grinding material should rangetrom a particle size of about1/4"-1s diameter, down to a size not to exceed about 40 mesh infineness. The inert grinding medium also functions as Percent Y Anamount of a heat storage medium aiding in maintaining uniformtemperatures in the bed of solids 7.

A portion of the bed of solids 7 is continuously or intermittentlywithdrawn through the bottom bed outlet 16 controlled by valve 17 or thetop bed outlet 18 controlled by valve 19, or both, and passed downthrough conduit 21 into Crusher designated by numeral 22, to reduce anyagglomerates and massive ore particles which resist the grinding actionof the inert material in the bed of solids 7. Crusher 22 may be aconventional roller crusher having rolls 23 spaced apart a distance ofapproximately 5/16-?/16 to avoid crushing the inert grinding medium. Thepreliminary treatment of the ore in chamber 6 facilitates attrition ofthe solids because of composition changes due to heating and reaction,internal stress due to thermal shock, and mechanical erosion.

The crushed ore from Crusher 22 is then returned to the uidized-driervessel 6 by means of elevator 24 which may be a conventionalheat-resistant, sealed, bucket elevator or other suitable conveyer.

The operation of the iluidized-drying chamber was described particularlywith reference to the treatment of large size raw untreated iron pyritesor pyrrhotite. The iluidized-drying operation in chamber 6 is alsoapplicable to the treatment of flotation concentrate, which, aspreviously mentioned, is a by-product from the mining industry' andgenerally consists of nely divided sulfide ore of below 60-80 mesh size.Flotation ore as received, is unsuitable for introduction into asuspension burner and must be given a preliminary treatment because itcontains appreciable amounts of moisture and is in the form ofagglomerates or clumps. Conventional practice is to preliminarily grindthe dotation ore in a ball mill and pass a non-oxidizing gas at atemperature of about 60G-700 F. through the otation ore to dry it. Thedried ground otation concentrate is then introduced into a suspensionburner. In the present invention, the flotation ore may be passed fromfeed hopper 2 down through screw feeder 3, conduits 4 and 5, intofluidized drying chamber 6 wherein it is subjected to tluidization andelutriation in a manner previously described. Some of the advantagesover the conventional practice of grinding and drying are (a) the oreparticles swept from the uidization chamber are partially oxidized,which reduces the amount of oxidation to be done in the suspensionburner, (b) the ore particles and `gas are preheated, which increasesthe burning capacity of the suspension burner. The net effect of theseadvantages are to increase the degree of desulfurization of ore in thesuspension burner, resulting in greater output of SO2 per unit ofcharged ore and a more useful cinder by-product.

When employing flotation concentrate as the feed charge to the fluidizeddrying chamber 6, it may be unnecessary to employ crusher 23 or toemploy it only intermittently to break up the agglomerates of ore whichare resistant to attrition in chamber 6.

The particles of partially roasted ore suspended in hot gassubstantially free from oxygen and containing SO2 are released from thetop of chamber 6, pass down through conduit 8 and exible hose 25 and upinto the bottom of suspension burner 26. Additional air from theatmosphere in amount suticient to cause complete oxidation of the ore isforced by air-blower 27 through conduit 28, ucommingled with the streamof hot gas containing suspended ore particles and the mixture passedupwardly through suspension roaster .26. If desired, only a portion ofthe air may be supplied by air-blower 27, the remainder of the airnecessary to effect substantially complete combustion being brought inas secondary air through an opening 29 controlled by valve 31 orplurality of such openings near the bottom of chamber 26. Ordinarily,thesuspension burner operates at slight subatmospheric pressure whichmakes it unnecessary to employ a blower for the introduction ofsecondary air through opening 29. The 'fine particles of"ore are blownupwardlythrough suspension burnerv 26 and discharged from the topthereof through outlet 32. During the upward passage of the oreparticles through suspension burner 26, the sulfide ore reacts with theoxygen YIto produce sulfur dioxide and iron oxide. As a result of thishighly exotherm-ic reaction, the temperature of the sol-ids in theroaster 26 is in excess of l800 F., generally between 20002400 F. Mostof the cinder is carried out of the suspension burner 26 through line32. Some of the coarse cinder settles to the bottom of chamber 26 andmay be discharged therefrom through line 33 and valve 34.

The gases and cinder discharging from the top of suspension burner 26through opening 32 pass through waste heat boiler 35 wherein most of thecinder settles out and is disc-harged through line 36 and valve 37.

Gases together with some cinder from waste heat boiler 35 pass throughopening 3S into cinder collector 39 wherein further settling of thecinder takes place to be dis charged through line 41 and valve 42. Thelgases leaving collector 39 are at a temperature of about 600-800 F.Blower 43 sucks the cooled SO2 containing gases from cinder collector 39through line 44 and directs them through conduit 45 to conventional gaspurication system and then contact sulfuric acid process for theproduction of sulfuric acid. A portion ofthe gases discharging throughline 45 are returned via line 46, valves 47 and 48 to the top ofsuspension burner 26. One of the purposes of returning cooled recyclegas to the top of the suspension burner is to maintain a temperatureatthe top of the burner near the outlet at about 1800 F. to retardfusion of the ore at fthe outlet of chamber 26. Another portion of therecycle SO2 gas -is directed through line 46, valve 49 and line 51 lintothe inlet of blower 11 wherein it passes upwardly together with airthrough the bed of solids 7 in chamber 6.

We have found that as a result of our two-stage fluidsuspension roastingoperation, coupled with classification, elutriation, drying andpreheating of the ore particles, that the cinder produced is lower insulfur content than normally produced in the conventional method ofsuspension burning, or alternatively, for the same sulfur content, Wecan obtain a greater throughput of ore as compared to conventionalsuspension roasting. An-

other advantage resulting from the use of our uidizedmesh; 8% of 65+l5mesh; 12% of -100-1-200 mesh;- and 28% of 200 mesh; and containing about4% moisture is introduced into a uidized drying chamberat the rate ofapproximately 161/2 net tons pyrrhotite per hour. The uidized-dryingchamber has a cross-sectional area of 25 square feet and a height ofapproximately 16 feet. Near the bottom of the fluidized-drying chamberis disposed perforated plate supporting a bed of inert sand mesh. Thedepth of the inert body is approximately lfoot. Air, in the amount of3400 C. F. M. standard con, dition together with 15% cooled recycle forcontrol, is passed under pressure of l p. s. i. g. into the bottom offluidized-drying chamber beneath the perforated plate passing upwardlythrough the bed of solids and inert mal terial, maintaining the bed in afluidized state at a temperature of 1400-1500" F. Approximately 10 feet'of void space above the turbulent bed of solids serves as dis-x;engagement volume for coarser particles. The finer par.v

composed of particles having a graduated size from'about' 174 diametergraduated down -to a minimum of .401

ticles,. i. e. particlesless: than 60.mesh, are swept lout ofithe-.chamber withl the gas; disclttargingv therefrom. Apor'Y tion ofythe dense phase of *thefbed of solids'at. thev rateof about. 5 tons`per. hour Cif-oreV are withdrawn| crushed and returned. to-the top oftheuidized-drying chamber. The

hot exit gas. from the. tiuidized-drying chamber containing suspendedfine ore particles, is passed, directly into the bottom of a suspensionburner where, together withadditional a-ir at the rate of about 14,000cubic feet. total per minute also introduced into` the bottom; of thesuspensionv burner, asy primary and secondary air, the fine particlesare blown upwardly rthrough the suspension burner and. roasted atatemperature of 1800-2400 F. The suspension burner has a diameter ofV 25feet and a height of 50 feet. SO2A containing; gas and cinder aredischarged from. the suspensionroaster, the cinder separated therefrom,the gas partially cooled andY -then directed to gas purificationand-further treatment into sulfuric acid. A portion of cooled gasl isrecycled tothe top of the suspension burner to maintain the ltemperatureat the top at about 1800"" F. Another portion of the recycle gas iscommingled with the. air introduced into the bottom of theuidized-drying chamber. The gras product leaving the suspension roastercontains approximately 12% SO2.v TheY cinder product has a sulfurcontent of about 0.4%, which cinder is suitable for use inV themanufacture ofk iron and steel.

Although certain preferred embodiments of the'invenltion have beendisclosed for purpose of illustration it will be evident that variouschanges and modifications may be made therein Without departing from thescope and spirit of thevinvention.

We claim:

l. A continuoustwo-stage duid-suspension process for convertingmetalsulfide ore selected from the group consisting of iron pyrites andpyrrhotite into sulfur dioxide and low-sulftry cinder which comprisesmaintaining a Y fluidized bed of divided sulfide ore particles supportedon a perforated plate in a first zone, introducing metal sulfiedforeinto said uidized bed at a rate sufiicientV to maintain a uidized bed insaid first zone, passing a stream of. oxygencontaining gas upwardlythrough the perforated plate and uidized bed at al velocity suicientlyhigh to maintain the solids in the bed of a particle size greater than40 mesh inV a'uidvstate and tofelutriate from the iiuidized bed solidsof particle size not greater than 40 mesh as a dispersed suspensionVcarriedby the stream of gas leaving theA top of the uidized; bed,regulating .the rate of introduction of ore` and oxygencontaining gasinto the first zone to maintain therein a temperature in excess of about800 F. and below 1800 F. thereby effecting drying and partial roastingof the ore, discharging the stream of gas containing the dispersedsuspension of particles not greater than 40 meshfrom the first zone at apoint above the iiuidized bed, passing said stream of gas containing thedispersed suspension of'particles not greater than 40 mesh withoutseparation of the dispersed particles from the gas through a secondsuspension-roasting zone larger than the rstzone inwhich second zone thedispersed suspension of particles are further roasted, introducingadditional oxygen-containing air into the supension-roasting zone tomaintain a temperature in excess of 1800 F. therein and to effectsubstantially complete oxidation of the particles of ore in dis'- persedsuspension, discharging SO2 containing. gas. and roastedv ore from thesuspension-roasting zone, and sepa rating cinder from the dischargedgas.

2. A continuous two-stage fluid-suspension process for converting metalsulfide ore selected from the group consisting of iron pyrites andpyrrhotite into sulfur dioxide and low-sulfur cinder which comprisesintroducing the orc into and maintaining a fluidized bed composed ofdivided sulfideore particles and particles of an` inertgrindin'glimediurn having al particle size within: the range' ofabourl/s-T' diameter to about 40'mesh suppported on aA perforated` plate inva ilSt4 Zone, passing a stream of gas containingY oxygen upwardlythrough the perforated plate uid state and to elutirate from theiiuidizedT bed solids of particle size not greater than 40 mesh as adispersed suspension carried by the stream of gas leaving the topV ofYthe uidized bed, regulating the rate of introduction ofY ore and gascontaining oxygen into the first zone to maintain therein a temperature`in excess of about 800 F. and below 1800" F. thereby effecting dryingand partial roasting of the ore, discharging the stream of gascontaining the dispersed suspension of particles not greater than'40mesh from the first zone at a point above the uidized bed, passingsaidstream of gas containing the dispersed suspension of particles notgreater than 40 mesh without separation of the dispersed particles fromthe gas through. a second suspension-roasting zone larger than the firstzone in which,v secondzone the dispersed suspension of particles arefurther roasted, introducing additional gas containing oxygen into thesuspensionroastingw zone to maintaina temperature in excess of l800 F.therein and toefect substantially complete oxidation of the particles ofore-in dispersed suspension, discharging SOz containing gasl and roastedore from the suspension-roasting Zone, and. separating cinder from the Ydischarged gas.

Y3. A continuous two-stage fluidesuspension process for converting iron`sulfide ore in to sulfur dioxide and lowsulfur cinder which' comprisesintroducing the ore into and maintaining a` uidized bed composedV ofdivided sulfide ore particles and particles of inert grindingmediurnVhaving a particle size WithinV the range` of about l/s" diameter toaboutv40'mesh sllPpOrte'd on arperforated plate in a first zone, passinga stream of gas containing oxygen upwardlythrough the perforatedplateand.- fluidized bed containing inert grinding medium and ore at avelocity suiiicientlyhighy to maintain the solids in theA bed of aVparticle size greater than 40'mesh in a fiuid state andi to elutriatefrom theiluidized bed solids of particle size not greater than 40 meshas agdispersed: suspension; carried by the stream of gas leavinglthe topof the iluidized bed, regulating the rate of introduction of oreand gascontaining oxygen into the first zone to maintain therein a temperaturein excess of about 800? F. and below 1800or F. thereby effectingdrying:andzpartial'roastingof the ore, discharging |the stream of gascontaining the dispersed suspension of particles not'greatcr. than40'mesh from the first zone atl a point above the uidized bed,withdrawing a portion of large size particles of ore from the uidizedbed of solids in the first zone, crushing said 'large particles,returning; said crushed ore to thev first zone for further contact withthe upwardly rising streamv of gas therein, passing said stream of gascontaining the dispersed suspension of particles not greater thanV 40mesh through a second suspension-roasting: zone larger than' the firstzone in whichv second zone the dispersed suspension'of particlesarefurtherfroas'ted, introducingl additional gas containing oxygen intothe suspension-roasting zone to maintain ak temperature in excess of1800o F. therein and to effect substantially complete oxidation of theparticles of ore in dispersed suspension, discharging- SO2 containingvgas'and roastedore from the suspensionroasting'zone, and separating:cinder from the discharged' gas. f

in a` first zone, V.passing a stream. ofg'a'scontaining oxygen' upwardlythrough theperforated plate andV fiuidi'zed bed 4. A continuoustwo-stage uid-suspension process foransioso containing inert grindingmedium and ore at a velocity sufficiently high to maintain the solids inthe bed of a particle size greater than 40 mesh in a fluid state and toelutriate from the fluidized bed solids of particle size not greaterthan 40 mesh as a dispersed suspension carried by the stream of gasleaving the top of the nidized bed, regulating the rate of introductionof ore and gas containing oxygen into the rst zone to maintain therein atemperature between about l300 F. and 1500 F., thereby eecting dryingand partial roasting of the ore, discharging the stream Cf gascontaining the dispersed suspension of particles not greater than 40mesh from the first zone at a point above the fluidized bed, withdrawinga portion of large size particles of ore from the fluidized bed ofsolids in the rst zone, crushing said large particles, returning saidcrushed ore to the first zone for further contact with the upwardlyrising stream of gas therein, passing said stream of gas containing thedispersed suspension of particles not greater than 40 mesh through asecond suspension-roasting zone larger than the rst zone in which secndzone the dispersed suspension of particles are further roasted,introducing additional gas containing oxygen into thesuspension-roasting zone to maintain a temperature in excess of 1830" F.therein and to effect substantially complete oxidation of the particlesof ore in dispersed suspension, discharging SO2 containing gas androasted ore from the suspension-roasting zone, separating cinder fromthe discharged gas, cooling the SO2 containing gas, and introducing aportion of the cooled SO2 containing gas into the rst zone below theperforated plate to provide a sufficiently high gas velocity to maintainthe solids as a uidized bed and to elutriate from the uidized bed finelydivided particles of ore of'a size not greater than 40 mesh.

5. A continuous two-stage fluid-suspension process for converting ironsulfide ore into sulfur dioxide and lowsulfnr cinder which comprisesintroducing the ore into and maintaining a fluidized bed composed ofdivided sulfide ore particles and particles of an inert grindingmaterial ranging in particle size from about li diameter down to a sizenot to exceed about 50 mesh in fineness supported on a perforated platein a first zone, passing a stream of gas containing oxygen upwardlythrough the perforated plate and fluidized bed containing inert grindingmedium and ore ata velocity snfliciently high to maintain the solids inthe bed of a particle size greater than 40 mesh in a fluid state `and toelutriate from the -lluidized bed solids of particle size not greaterthan 40 mesh as a dispersed suspension carried by the stream of gasleaving the top of the tluidized bed, regulating the rate ofintroduction of ore and gas containing oxygen into the first zone tomaintain therein a temperature between 1300 F. and 1500 F.,

thereby effecting drying and partial roasting of the ore, dischargingthe stream of gas containing the dispersed suspension of particles notgreater than 40 mesh from the first zone at a point above the fluidizedbed, withdrawing a portion of large size particles of ore, crushing saidlarge particles, returning said crushed ore to the first zone forfurther contact with the upwardly rising stream of gas therein, passingsaid stream of gas containing the dispersed suspension of particles notgreater than 40 mesh through a second suspension-roasting zone largerthan the rst zone in which second zone the dispersed suspension ofparticles are further roasted, introducing `additional gas containingoxygen into the suspension-roasting zone to maintain a temperature inexcess of 1800 F. therein and to effect substantially complete oxidationof the particles of ore in dispersed suspension, discharging SO2containing gas and roasted ore from the suspension-roasting zone,separating cinder from the discharged gas, cooling the SO2 containinggas, recycling a portion of the cooled SO2 containing gas to thesuspension-roasting zone at a point near the discharge of gas therefromto aid in maintaining a temperature of approximately 1800 F. at saidpoint of discharge, and introducing a portion of the cooled SO2`containing gas into the first zone below the perforated plate to providea sufficiently high gas velocity to maintain the solids as a fluidizedbed and to elutriate from the tluidized bed finely divided particles ofore of a size not greater than 40 mesh.

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1. A CONTINUOUS TWO-STAGE FLUID-SYSPENSION PROCESS FOR CONVERTING METALSULFIDE ORE SELECTED FROM THE GROUP CONSISTING OF IRON PYRITED ANDPYRRHOTITE INTO SULFUR DIOXIDE AND LOW-SULFUR CINDER WHICH COMPRISESMAINTAINING A FLUIDIZED BED OF DIVIDED SULFIDE ORE PARTICLES SUPPORTEDON A PERFORATED PLATE IN A FIRST ZONE, INTRODUCING METAL SULFIDE OREINTO SAID FLUIDIZED BED AT A RATE SUFFICIENT TO MAINTAIN A FLUIDIZED BEDIN SAID FIRST ZONE, PASSING A STREAM OF OXYGEN-CONTAINING GAS UPWARDLYTHROUGH THE PERFORATED PLATE AND FLUIDIZED BED AT A VELOCITYSUFFICIENTLY HIGH TO MAINTAIN THE SOLIDS IN THE BED OF A PARTICLE SIZEGREATER THAN 40 MESH IN A FLUID STATE AND TO ELUTRIATE FROM THEFLUIDIZED BED SOLIDS OF PARTICLE SIZE NOT GREATER THAN 40 MESH AS ADISPERSED SUSPENSION CARRIED BY THE STREAM OF GAS LEAVING THE TOP OF THEFLUIDIZED BED, REGULATING THE RATE OF INTRODUCTION OF ORE ANDOXYGENCONTAINING GAS INTO THE FIRST ZONE TO MAINTAIN THEREIN ATEMPERATURE IN EXCESS OF ABOUT 800* F. AND BELOW 1800* F. THEREBYEFFECTING DRYING AND PARTIAL ROASTING OF THE ORE, DISCHARGING THE STREAMOF GAS CONTAINING THE DISPERSED